There are circumstances in which it would be desirable to be able to alter the effective length of a manually operable lever arm. Two constructions for adjusting the length of a lever arm are shown in U.S. Pat. No. 4,582,298 and in US patent application US20060196303A1. U.S. Pat. No. 4,582,298 discloses a yacht winch assembly in which the winch crank arms are telescopic to permit the arms to be increased in length by releasing a spring-biased catch which is capable of holding the arm in either a short or long condition. The user chooses whether to increase the winch arm length or to reduce it. US 20060196303A1 discloses a handle of adjustable length for operating a screw jack, the handle having a slidable connection with the rotatable drive of the jack. The effective length of the handle can be manually adjusted.
Others have sought to create articulated handles on spanners, wrenches and the like to collapse for ease of storage or to bend to allow access of the tool to awkward to reach areas, such as to reach pipe couplings behind sink units et cetera. Examples include U.S. Pat. No. 4,672,805, U.S. Pat. No. 4,606,247, U.S. Pat. No. 6,412,374 and U.S. Pat. No. 7,343,847. A car door window handle of similar design is shown in DE 1555819 and articulates to flex out of harm's way in a crash. All of the afore-mentioned devices have the handle lever lying in use in a plane orthogonal to the rotating axis of the item to be rotated by the tool and are designed for the lever handle to curl or bend away from that plane not to curl in that plane. In each case when the lever handle is curled it does not curl around the rotating axis/drive axis of the tool. These devices do not provide for any substantial adjustment of the length of the lever handle for adjusting leverage.
The inventive lever arm assembly of variable radius of the present invention stems in part from some work aimed at providing a lever arm assembly in which spring biasing is used to assist in adjusting the effective length of the lever arm. However, the invention also encompasses some advantageous constructions that do not necessarily employ spring-biasing. The present invention seeks to overcome the limitations of existing lever arm devices to provide for substantial adjustment in leverage for a range of different uses.